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ORGANISM AND POPULATION
Question 1:
How is diapause different from hibernation?
Answer 1:
Diapause is a stage of suspended development to cope with unfavourable
conditions. Many species of Zooplankton and insects exhibit diapause to tide
over adverse climatic conditions during their development.
Hibernation or winter sleep is a resting stage where in animals escape winters
(cold) by hiding themselves in their shelters. They escape the winter season by
entering a state of inactivity by slowing their metabolism. The phenomenon of
hibernation is exhibited by bats, squirrels, and other rodents.
Question 2:
If a marine fish is placed in a fresh water aquarium, will the fish be able to
survive? Why or why not?
Answer 2:
If a marine fish is placed in a fresh water aquarium, then its chances of survival
will diminish. This is because their bodies are adapted to high salt
concentrations of the marine environment. In fresh water conditions, they are
unable to regulate the water entering their body (through osmosis). Water enters
their body due to the hypotonic environment outside. This results in the swelling
up of the body, eventually leading to the death of the marine fish.
Question 3:
Define phenotypic adaptation. Give one example.
Answer 3:
Phenotypic adaptation involves changes in the body of an organism in response
to genetic mutation or certain environmental changes. These responsive
adjustments occur in an organism in order to cope with environmental
conditions present in their natural habitats. For example, desert plants have thick
cuticles and sunken stomata on the surface of their leaves to prevent
transpiration. Similarly, elephants have long ears that act as thermoregulators.
Question 4:
Most living organisms cannot survive at temperature above 45°C°. How are
some microbes able to live in habitats with temperatures exceeding 100°C?
Answer 4:
Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water
springs and deep sea hydrothermal vents. They are able to survive in high
temperatures (which far exceed 100°C) because their bodies have adapted to
such environmental conditions. These organisms contain specialized thermoresistant enzymes, which carry out metabolic functions that do not get destroyed
at such high temperatures.
Question 5:
List the attributes that populations but not individuals possess.
Answer 5:
A population can be defined as a group of individuals of the same species
residing in a particular geographical area at a particular time and functioning as
a unit. For example, all human beings living at a particular place at a particular
time constitute the population of humans.
The main attributes or characteristics of a population residing in a given area are:

Birth rate (Natality): It is the ratio of live births in an area to the population
area. It is expressed as the number of individuals
 added to the
 ofan
population with respect to the members of the population.

Death rate (Mortality): It is the ratio of deaths in an area to the population
area. It is expressed 
as the loss of individuals with respect to the
 ofan
members of the population.



Sex ratio: It is the number of males or females per thousand individuals.

Age Distribution: It is the percentage of individuals of different ages in a
givenpopulation. At any given time, the population is composed of
individuals that are present in various age groups. The age distribution
 pattern is commonly represented through age pyramids.

Population density: It is defined as the number 
of individuals of a
populationpresent per unit area at a given time.
Question 6:
If a population growing exponentially double in size in 3 years, what is the
intrinsic rate of increase (r) of the population?
Answer 6:
A population grows exponentially if sufficient amounts of food resources are
available to the individual. Its exponential growth can be calculated by the
following integral form of the exponential growth equation:
rt
Nt= No e
Where,
Nt= Population density after time t
NO= Population density at time zero
r = Intrinsic rate of natural increase
e = Base of natural logarithms
(2.71828)
From the above equation, we can calculate the intrinsic rate of increase (r) of a
population.
Now, as per the question,
Present population density = x
Then,
Population density after two years = 2x
t = 3 years
Substituting these values in the formula, we get:
⇒
⇒
⇒
3r
2x = x e
3r
2=e
log 2 = 3r log e
Hence, the intrinsic rate of increase for the above illustrated population is 0.2311.
Question 7:
Name important defence mechanisms in plants against herbivory.
Answer 7:
Severalplants have evolved various mechanisms both morphological and
chemical to protect themselves against herbivory.
Morphological defence mechanisms:

Cactus leaves (Opuntia) are modified
 into sharp spines (thorns) to deter
herbivores from feeding on them.



Sharp thorns along with leaves are present in Acacia to deter herbivores.

In some plants, the margins of their leaves
are spiny or have sharp edges that
prevent herbivores from feeding on them.
Chemical defence mechanisms:

parts of Calotropis weeds contain toxic
cardiac glycosides, which can
 All
prove to be fatal if ingested by herbivores.

Chemical substances such as nicotine, caffeine,
 quinine, and opium are
produced in plants as a part of self-defence.
Question 8:
An orchid plant is growing on the branch of mango tree. How do you describe
this interaction between the orchid and the mango tree?
Answer 8:
An orchid growing on the branch of a mango tree is an epiphyte. Epiphytes are
plants growing on other plants which however, do not derive nutrition from
them. Therefore, the relationship between a mango tree and an orchid is an
example of commensalisms, where one species gets benefited while the other
remains unaffected. In the above interaction, the orchid is benefited as it gets
support while the mango tree remains unaffected.
Question 9:
What is the ecological principle behind the biological control method of
managing with pest insects?
Answer 9:
The basis of various biological control methods is on the concept of predation.
Predation is a biological interaction between the predator and the prey, whereby
the predator feeds on the prey. Hence, the predators regulate the population of
preys in a habitat, thereby helping in the management of pest insects.
Question 10:
Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms
Answer 10:
(a) Hibernation and Aestivation
Hibernation
Aestivation
1. Hibernation is a state of reduced 1. Aestivation is a state of reduced
activity in some organisms to
activity in some organisms to
escape cold winter conditions.
escape desiccation due to heat in
summers.
2. Bears and squirrels inhabiting 2. Fishes and snails are examples of
cold regions are examples of
organisms aestivating
during
animals that hibernate during
summers.
winters.
(b) Ectotherms and Endotherms
Ectotherms
Endotherms
1. Ectotherms are cold blooded
1. Endotherms are warm blooded
animals. Their temperature varies
animals. They
maintain a
with their surroundings.
constant body temperature.
2. Fishes, amphibians, and reptiles are 2 Birds and mammals
are
ectothermal animals.
endothermal animals.
Question 11:
Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals.
(a) Adaptations of desert plants and animals

Adaptations of desert plants
Plants found in deserts are well adapted to cope with harsh desert conditions such
as water scarcity and scorching heat. Plants have an extensive root system to tap
underground water. They bear thick cuticles and sunken stomata on the surface of
their leaves to reduce transpiration. In Opuntia, the leaves are entirely modified
into spines and photosynthesis is carried out by green stems. Desert plants have
special pathways to synthesize food, called CAM (C4 pathway). It enables the
stomata to remain closed during the day to reduce the loss of water through
transpiration.

Adaptations of desert animals

Animals found in deserts such as desert kangaroo rats, lizards, snakes, etc. are
well adapted to their habitat. The kangaroo rat found in the deserts of Arizona
never drinks water in its life. It has the ability to concentrate its urine to
conserve water. Desert lizards and snakes bask in the sun during early morning
and burrow themselves in the sand during afternoons to escape the heat of the
day. These adaptations occur in desert animals to prevent the loss of water.
(b) Adaptations of plants to water scarcity
Plants found in deserts are well adapted to cope with water scarcity and scorching
heat of the desert. Plants have an extensive root system to tap underground water.
They bear thick cuticles and sunken stomata on the surface of their leaves to reduce
transpiration. In Opuntia, the leaves are modified into spines and the process of
photosynthesis is carried out by green stems. Desert plants have special pathways
to synthesize food, called CAM (C4 pathway). It enables their stomata to remain
closed during the day to reduce water loss by transpiration.
(c) Behavioural adaptations in animals
Certain organisms are affected by temperature variations. These organisms
undergo adaptations such as hibernation, aestivation, migration, etc. to escape
environmental stress to suit their natural habitat. These adaptations in the
behaviour of an organism are called behavioural adaptations. For example,
ectothermal animals and certain endotherms exhibit behavioral adaptations.
Ectotherms are cold blooded animals such as fish, amphibians, reptiles, etc.
Their temperature varies with their surroundings. For example, the desert lizard
basks in the sun during early hours when the temperature is quite low. However,
as the temperature begins to rise, the lizard burrows itself inside the sand to
escape the scorching sun. Similar burrowing strategies are exhibited by other
desert animals. Certain endotherms (warm-blooded animals) such as birds and
mammals escape cold and hot weather conditions by hibernating during winters
and aestivating during summers. They hide themselves in shelters such as caves,
burrows, etc. to protect against temperature variations.
(d) Importance of light to plants
Sunlight acts as the ultimate source of energy for plants. Plants are autotrophic
organisms, which need light for carrying out the process of photosynthesis. Light
also plays an important role in generating photoperiodic responses occurring in
plants. Plants respond to changes in intensity of light during various seasons to
meet their photoperiodic requirements for flowering. Light also plays an important
role in aquatic habitats for vertical distribution of plants in the sea.
(e) Effects of temperature or water scarcity and the adaptations of animals.
Temperature is the most important ecological factor. Average temperature on
the Earth varies from one place to another. These variations in temperature
affect the distribution of animals on the Earth. Animals that can tolerate a wide
range of temperature are called eurythermals. Those which can tolerate a narrow
range of temperature are called stenothermal animals. Animals also undergo
adaptations to suit their natural habitats. For example, animals found in colder
areas have shorter ears and limbs that prevent the loss of heat from their body.
Also, animals found in Polar regions have thick layers of fat below their skin
and thick coats of fur to prevent the loss of heat.
Some organisms exhibit various behavioural changes to suit their natural habitat.
These adaptations present in the behaviour of an organism to escape environmental
stresses are called behavioural adaptations. For example, desert lizards are
ectotherms. This means that they do not have a temperature regulatory mechanism
to escape temperature variations. These lizards bask in the sun during early hours
when the temperature is quite low. As the temperature begins to increase, the lizard
burrows itself inside the sand to escape the scorching sun. Similar burrowing
strategy is seen in other desert animals.
Water scarcity is another factor that forces animals to undergo certain adaptations
to suit their natural habitat. Animals found in deserts such as desert kangaroo rats,
lizards, snakes, etc. are well adapted to stay in their habitat. The kangaroo rat found
in the deserts of Arizona never drinks water in its life. It has the ability to
concentrate its urine to conserve water. Desert lizards and snakes bask in the sun
during early morning and burrow in the sand as the temperature rises to escape the
heat of the day. Such adaptations can be seen to prevent the loss of water.
Question 12:
Define decomposition and describe the processes and products of decomposition.
Answer 12:
Decomposition is the process that involves the breakdown of complex organic
matter or biomass from the body of dead plants and animals with the help of
decomposers into inorganic raw materials such as carbon dioxide, water, and
other nutrients. The various processes involved in decomposition are as follows:

Fragmentation: It is the first step in the process of decomposition.
Itinvolves
the breakdown of detritus
into smaller pieces by the action of


detritivores such as earthworms.

Leaching: It is a process where the
water soluble nutrients go down intothe soil

layers and get locked as unavailable salts.

Catabolism: It is a process in which
 bacteria and fungi degrade detritusthrough

various enzymes into smaller pieces.

Humification: The next step is humification which leads to the
formationof
a darkcoloured colloidal
substance called humus, which acts as


reservoir of nutrients for plants.

Mineralization: The humus is further degraded by the action of
microbes,which finally leads to the release of inorganic nutrients into the soil. This
process of releasing
inorganic nutrients from the humus is known as


mineralization.
Decomposition produces a dark coloured, nutrient-rich substance called humus.
Humus finally degrades and releases
 inorganic raw materials such as CO2,
water, and other nutrient in the soil.
Question 13:
Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of benthic zone
(a) Endothermic animal: Birds such as crows, sparrows, pigeons, cranes, etc.
and mammals such as bears, cows, rats, rabbits, etc. are endothermic animals.
(b) Ectothermic animal: Fishes such as sharks, amphibians such as frogs, and
reptiles such as tortoise, snakes, and lizards are ectothermic animals.
(c) Organism of benthic zone: Decomposing bacteria is an example of an
organism found in the benthic zone of a water body.
)
Question 14:
Define population and community.
Answer 14:
Population:
A population can be defined as a group of individuals of the same species
residing in a particular geographical area at a particular time and functioning as
a unit. For example, all human beings living at a particular place at a particular
time constitute the population of humans.
Community:
A community is defined as a group of individuals of different species, living
within a certain geographical area. Such individuals can be similar or dissimilar,
but cannot reproduce with the members of other species.
Question 15:
Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition
(a) Commensalism: Commensalism is an interaction between two species
inwhich one species gets benefited while the other remains unaffected. An
orchid growing on the branches of a mango tree and barnacles attached to the
body of whales are examples of commensalisms.
(b) Parasitism: It is an interaction between two species in which one
species(usually smaller) gets positively affected, while the other species (usually
larger) is negatively affected. An example of this is liver fluke. Liver fluke is a
parasite that lives inside the liver of the host body and derives nutrition from it.
Hence, the parasite is benefited as it derives nutrition from the host, while the host
is negatively affected as the parasite reduces the host fitness, making its body
weak.
(c) Camouflage: It is a strategy adapted by prey species to escape
theirpredators. Organisms are cryptically coloured so that they can easily
mingle in their surroundings and escape their predators. Many species of frogs
and insects camouflage in their surroundings and escape their predators.
(d) Mutualism: It is an interaction between two species in which both species
involved are benefited. For example, lichens show a mutual symbiotic
relationship between fungi and blue green algae, where both are equally
benefited from each other.
(e) Interspecific competition: It is an interaction between individuals
ofdifferent species where both species get negatively affected. For example, the
competition between flamingos and resident fishes in South American lakes for
common food resources i.e., zooplankton.
Question 16:
With the help of suitable diagram describe the logistic population growth curve.
Answer 16:
The logistic population growth curve is commonly observed in yeast cells that
are grown under laboratory conditions. It includes five phases: the lag phase,
positive acceleration phase, exponential phase, negative acceleration phase, and
stationary phase.

Lag phase: Initially, the population of
the yeast cell is very small. This isbecause

of the limited resource present in the habitat.

Positive acceleration phase: During this phase, the yeast cell adapts to
thenew
environment and starts increasing its population. 
However, at the

beginning of this phase, the growth of the cell is very limited.

Exponential phase: During this phase, the population of the yeast
cellincreases suddenly due to rapid growth. The population grows exponentially
due to the availability of sufficient food resources, constant environment, and
the absence
 of any interspecific competition. As a result, the curve rises steeply

upwards.

Negative
acceleration
phase:
During
this
phase,
the
environmentalresistance increases and the growth rate of the population
decreases. This occurs
 due to an increased competition among the yeast cells for

food and shelter.

Stationary phase: During this phase, the population becomes stable.
Thenumber of cells produced in a population equals the number of cells that die.
Also, the population 
of the species is said to have reached nature’s carryingcapacity in its habitat.
A Verhulst − pearl logistic curve is also known as an S-shaped growth curve.
Question 17:
Select the statement which explains best parasitism.
(a) One organism is benefited.
(b) Both the organisms are benefited.
(c) One organism is benefited, other is not affected.
(d) One organism is benefited, other is affected.
(d) One organism is benefited, other is affected.
Parasitism is an interaction between two species in which one species (parasite)
derives benefit while the other species (host) is harmed. For example, ticks and
lice (parasites) present on the human body represent this interaction where in
the parasites receive benefit (as they derive nourishment by feeding on the
blood of humans). On the other hand, these parasites reduce host fitness and
cause harm to the human body.
Question 18:
List any three important characteristics of a population and explain
Answer 18:
A population can be defined as a group of individuals of the same species,
residing in a particular geographical area at a particular time and functioning as
a unit. For example, all human beings living at a particular place at a particular
time constitute the population of humans.
Three important characteristics of a population are:

Birth rate (Natality): It is the ratio of live births in an area to the
populationof
an area. It is expressed as the number of individuals
added to the


population with respect to the members of the population.

Death rate (Mortality): It is the ratio of deaths in an area to the
populationof
an area. It is expressed
 as the loss of individuals with respect to

the members of the population.

Age Distribution: It is the percentage of individuals of different ages in
agiven population. At any given time, a population is composed of individuals
that are present in various age groups.
 The age distribution pattern is commonly
represented through age pyramids.